Your Eyes Can Write
Optics & Photonics Focus
Volume 18 Story 5 - 19/12/2012

The reverse phi motion optical illusion

Rapid changes of brightness engender a sensation that an object is moving in a direction opposite to the one in which it is actually moving. Here, when the circles change from black to white on alternate frames, they appear to be moving counterclockwise, while in reality they are actually moving clockwise, as you will notice if you focus (your attention) on one of them.
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The <i>reverse phi motion</i> optical illusion. Rapid changes of brightness engender a sensation that an object is moving in a direction opposite to the one in which it is actually moving. Here, when the circles change from black to white on alternate frames, they appear to be moving counterclockwise, while in reality they are actually moving clockwise, as you will notice if you focus (your attention) on one of them.